A better C64 Transmission

At BWR we’ve been frustrated with the Lotus transmission since 2006. As we add power and grip the C64 transmissions break. It is pretty robust given that it was designed for far less power than the forced induction cars we are running around with today. However we’ve broken over 10 transmissions in our XP car over the years and many others on track. We do a lot of transmission service work for the lotus community.

There are several issues with this box:

For Track Cars:
1. 1st and 2nd are too short, especially for a supercharged or turbo car.

2. The spacing is pretty wide causing RPM drops that make the car fall off the Big Cam

3. The wide spacing also forces the car out of the power band in higher gears as the aero load increases.

4. 3rd and 4th gears are prone to failure in road raced cars.

For AutoX Cars:
1. 1st and 2nd are too short at 43mph and 67mph for a boosted car.(Assumes stock tire height)

2. Ring and Pinions are known to fail in Pro Solo events at the drag start.

Other Options:
There some other gear sets, but we don’t believe they address these issues very well. Additionally, there is the Quaife sequential and H-pattern Dog Box. They have their issues too. We’ve re-designed an input shaft to fix the weak design from Quaife having broken 2. They are also dog-engagement, not sychro, so streetability is poor.

The e153 Transmission is an option, but it is only 5 speed, requires significant changes in the engine bay such as shifting the engine 2” to the right, and the gear spacing is huge. Lastly, it weighs 30lbs more than the C64.

Given that the C64-based Quaife sequential(with fixed input shaft) has been holding up well to track(Phil’s TT1 car & many others) and Extreme autox duty(my XP car), we believe with better design, heat treatment, and metallurgy we can build a better C64 to meet the needs of today’s forced induction lotus crowd.

I worked over this many times looking for ways to get all the “happy buttons” for all the different use cases. Once I had it narrowed down I got a lot of great input from Phil at BOE on the track-day side.

Our goals were to fix the issues above and add the following features:

1. Make 1st and 2nd tall enough to be usable. 2nd needs to be about 76mph for the AutoX guys.

2. Reduce the spacing between 2-5th to stay in the power band on the track, reduce synchro wear, and keep the engine on boil with increasing aero load.

3. Make 3rd and 4th wider for more strength.

4. Provide a stronger ring & pinion option for drag, pro-solo, or aggressive curb hopping.

5. Use existing synchros and 5th & 6th gear keep costs down (these gears don’t break) and pour the savings into superior quality materials, design, and heat treatment.

6. Keep the gears semi-helical for streetability.

7. Work with an experienced race gear supplier with success in drag and road racing.

Together, we went through a lot of different versions and have finally nailed down a winner.

It looks like this:
- Stock Trans with Stock tires at 8500rpm has 1st going to 43mph and 2nd to 67mph.

- BWR Gears, stock tires, stock Final Drive: 1st at 59mph and 2nd at 81mph.

- BWR Gears, stock tires with new Final drive: 1st at 56mph and 2nd at 76mph.

RPM drops stock vs BWR:
Stock BWR
1-2 2996 2283
2-3 2359 2140
3-4 1808 1447
4-5 1822 1071
5-6 937 937

There are some other interesting options here:

- 59mph in 1st will help hook up all the power and make stoplight battles better.

- Running 15” wheels and 23” tall Hoosiers in the back yields a 148mph top speed and really close ratio NA track attack option.

- Using the Celica taller 6th gear with stock tires means that 5th tops out at 151mph with stock Final drive or 141 with BWR FD, but still has a cruise gear taller than the lotus 6th for the drive home so you don’t buzz your brains out!

- FI autox guys have a useable 1st and the 76mph 2nd with 275/35R17 Hoosiers!

This is still a few months out. It won’t be the cheapest option, but we think it will be the lightest/best option.

:coolnana: